On 11/11/2014 2:42 PM, Lostgallifreyan wrote:
Wimpie wrote in :

Never mind Maxwell, why is no-one asking "why is an electromagnet not
used as an antenna when driven by AC?" That should be a basic reality
check because I've neve heard of such a thing working, and if it did it
would be widely known.

You may know that an AC current through a loop does generate near
fields, and far (EM radiation) fields. This follows from Maxwell's
equations. The solution for radiated power from a loop carrying AC
current is:


I did know, but I didn't think it through. What I had in mind was the kind
of electromagnet usually used to simulate a magnet, one with a big
lump magnetic material to guid the flux and concentrate it, etc. I imagine
the moment you do that, you get closer to a normal magnet, but it probably
makes the coil unusable as an antenna at the same time.

I think there are a lot of things you don't think through, lol. Ever
hear of a ferrite core antenna? Not much different. Why would an iron
core make a poor antenna?

--

Rick